With the premise that radical new departures in molecular recognition are unlikely to result from continued development of simple macrocyclic model systems, we have embarked on a synthetic program directed at new molecular shapes. Our intent is to incorporate in these designs a structural feature common to enzymes, receptors and antibodies: the convergence of functional groups to form an active site. The strategy by which this is accomplished uses a molecular cleft. The prototypes of the new systems are dicarboxylic acids which show an unprecedented affinity for molecules of complementary size, shape and functionality. Our initial studies indicate that the convergence of the carboxyl groups is the key to this selectivity. We intend to develop these and related structures as model receptors and test their ability to recognize substrates of specified structure. By derivatizing the acid functions, groups complementary to the target substrates can be incorporated into the lining of the cleft. Molecular modeling, using computer graphics, is expected to be an efficient screen for likely structural fits. Specific problems to be addressed are: 1) developing selective peracids, 2) recognition of asymmetric centers, 3) shape-specific binding of phosphoric, carboxylic and amine functions and 4) recognition of specific amino acid and peptide side chains.